Hitherto, a seal chain is used as transmitting and conveying means used in dusty atmosphere. The seal chain is provided with a seal mechanism which is interposed between inner and outer link plates to prevent lubricant such as grease entrapped in a bearing portion composed of an outer peripheral surface of a pin and an inner peripheral surface of a bush from leaking to the outside and foreign materials from entering from the outside. An annular resilient sealing member or an annular rigid sealing member such as an O-ring is used in general for the seal mechanism.
Still more, in order to improve the sealing function further, there is proposed a seal chain as shown in FIG. 7, having a seal mechanism 530 disposed between inner and outer link plates 511 and 521, which are both mounted on a pin 522 as shown in FIG. 7. The seal mechanism 530 includes a resilient ring 531, a seal ring 532 disposed outside of the resilient ring 531 and pressed against an opposed surface of the outer link plate 521, a tongued resin annular sealing member 533 disposed outside of the seal ring 532 and pressed against an opposed surface of the inner link plate 511, a ring-like plate 534 spaced from the outside of the tongued resin annular sealing member 533 and fixed to the opposed surface of the outer link plate 52. When the gap between the inner and outer link plates 511 and 521 fluctuates, for example when the seal chain 500 is in operation, the seal chain keeps its sealing performance by moving the seal mechanism 530 corresponding to the fluctuations of the gap between the inner and outer link plates 511 and 521. This movement is permitted by deformation of the resilient ring 531 and the tongued resin annular sealing member 533 or by a mutual sliding action between an inner peripheral surface of a base end portion of the tongued resin annular sealing member 533 and an outer peripheral surface of the seal ring 532, for example as disclosed in Japanese Patent Application Laid-open No. 2008-157423 and Japanese Utility Model Application Laid-open No. H5-1717.
However, although the seal mechanism 530 as described in Application No. 2008-157423 functions without trouble when the gap between the outer and inner link plates 521 and 511 changes in a direction of a center axis of the pin 522, i.e., in an axial direction (thrust direction), no consideration is given as for positional gap in a direction orthogonal to the direction of the center axis of the pin 522, i.e., in a radial direction which is the longitudinal direct of the chain.
While chains in general including a seal chain are used while being tensioned in a longitudinal direction, the chain elongates (extends) in the longitudinal direction when the chain is used in such a state for a long period of time.
One factor of such elongation is a gap (so-called misalignment) produced between the center axis of the pin 522 and a center axis of a bush 512 when the pin 522 and the bush 512 wear due to the tension applied in the longitudinal direction of the chain. However, no seal mechanism used in the prior art seal chains has been what takes special technological measures corresponding to the misalignment caused in the radial direction between the pin 522 and the bush 512.
Accordingly, if the misalignment as described above occurs in the prior art seal mechanism as described in Application No. 2008-157423, excessive force might be applied to the resilient ring 531 and the tongued resin annular sealing member 533, thus wearing or damaging the seal mechanism 530 and reducing the sealing performance. Due to that, it has been necessary to carry out maintenance works within a relatively short period of time.
Still more, relative positions of the outer and inner links normally change during operation of the chain and a volume of a spot where lubricant is entrapped such as a gap between the outer and inner link plates also always locally changes during operation of the chain.
Then, pressure often increases locally due to this local volume change.
Although the lubricant will not leak out of the seal mechanism in most cases, because the lubricant moves from a spot whose volume is reduced to another spot whose volume is increased, the movement of the lubricant becomes late in moving between the spots whose volumes fluctuate and the pressure often increases locally, though temporarily, if the fluctuation of the volume occurs in a short period of time. Accordingly, the prior art seal chain has a problem that the seal mechanism might be deformed and the lubricant might leak out if such increase of pressure occurs near the seal mechanism.